As a model railroader that also prints/sells 3d printed buildings... it depends. The larger the print, the more likely you'll have a slight defect. You'll find a lot of folks who sell for HO scale, but not a lot in O scale due to the size requirements.
You need to watch out for nozzle print size and material too. ABS and PETG is stronger, but harder to sand if you need to. Wood PLA is the easiest to sand and one of the most resistant to warping. Smaller nozzles like .3mm or .2mm (or less) give greater detail, but .4mm I would consider standard if your ordering a building or something (and wont be crazy expensive).
Don't expect too much out of brick molded printed parts, that's hit or miss unless the producer is a perfectionist. Clapboard or shingles are easier to get right.
At the end of the day, your paying for something you might not (without a lot of work) be able to model yourself. If its a building, then your paying for the scaling/plans/knowledge that its designed to be 1:48.
While filament isn't the most expensive (unless during covid haha), you also pay for the printing time and risk of mistakes. If the printer ruins a print, the producer might have to eat the costs of trying again (that risk cost is passed along to the consumer via increased prices across the board).
In short, any producer of 3d printed items that's reputable wont sell you something they are not proud of, or they will provide sample photos of their 'average' printing quality. You might get a slight bit of warp, or a minor defect, but that's the cost of your unique structure.
